Television receivers which feature picture-in-picture processing known. In such receivers an inset or "small" picture to be displayed within an area of a "main" or "large" picture is subjected to vertical and horizontal compression by means of selective storage and retrieval from a memory and the compressed picture video signal is inserted within an area of the main picture video signal by means of a multiplex switched that is controlled by timing signals provided by the picture in picture compression processor. Examples of picture in picture compression processors are described, for example, by D;. L. McNeely and R. T. Fling in U.S. Pat. No. 4,890,162 which issued Dec. 26, 1989 and by E. D. Romesburg in U.S. Pat. No. 4,768,083 which issued Aug. 30, 1988.
Non-linear video signal processors are known wherein a video signal is subjected to non-linear amplification within selected portions of the video signal range for providing improved detail in displayed images. O. H. Shade, for example, describes a non-linear video processor featuring both so-called "black stretch" and "white stretch" processing for improving detail in the darker and lighter areas of displayed images in U.S. Pat. No. 2,760,008 which issued Aug. 21, 1956. More recently, integrated circuits have become available providing non-linear picture enhancement functions. An example of such an integrated circuit is the type CX20125 "dynamic picture processing" integrated circuit manufactured by Sony Corp. This integrated circuit provides both "black stretch" processing for improving detail in darker picture areas and also provides a so-called "auto-pedestal" processing function. The auto-pedestal function may be used to adaptively adjust the brightness of a displayed image by inserting a "blacker-than-black" variable amplitude pulse during the back-porch region of the luminance signal. The brightness of a displayed image is altered because the "auto-pedestal" function changes the relationship between the clamping level of a "back-porch" clamp and the level of the video signal which is clamped.
It has been recognized as being desirable to provide both picture in picture processing and non-linear video signal processing (particularly "black stretch" processing) in a television receiver. An example is the Model CTC-169 color television receiver manufactured by Thomson Consumer Electronics Inc. A detailed block diagram of this receiver is shown in FIG. 1 herein and identified as "Prior Art". In this receiver, non-linear (e.g., black stretch) processing is applied to the main video signal prior to the insertion of the compressed auxiliary video signal by the multiplex switch that combines the main and compressed video signals for display.
In more detail, the receiver 10 of FIG. 1 includes an antenna input terminal (ANT) for receiving an RF video input signal S1 and an auxiliary input terminal (AUX) for receiving a baseband video input signal S2. Signal S1 is applied to a tuner and IF processing unit 12 which tunes and demodulates signal S1 to provide another baseband signal S3. A selector switch 14 selects one of signals S2 and S3 as a main video signal S4 for processing and selects the other of signals S2 and S3 as an "inset" video signal S5 for processing. The main video signal S4 is applied to an output terminal 15 labeled "Selected Video Out". This terminal is available for the user to facilitate recording of the main video signal selected by switch 14. The main video signal S4 is also applied to a luminance chrominance signal separation filter 16 that provides separated luminance and chrominance output signals Y1 and C1. The inset video signal S5 is applied to a picture in picture processor 18 that compresses signal S5 vertically and horizontally and provides compressed luminance (Y2) and chrominance (C2) output signals. The main luminance signal Y1 is applied to a non-linear processor 20 which subjects the Y1 signal to black stretch processing for improving detail in low brightness areas of the main picture by applying greater amplification to low level signals than to high level signals. In practice, the processor used is the Sony type CX20125 dynamic picture processor previously discussed. The non-linearly processed main luminance signal Y1', the main chrominance signal C1, and the compressed inset video components Y2 and C2 are applied to a multiplex switch 22 (e.g., a type CD4053 CMOS IC) controlled by a selection signal S6 which inserts the inset video signal components Y2, C2 within a portion of the area defined by the processed main video signal components Y1', C1 to provide picture in picture output signal components Y3 and C3.which, in turn, are applied to a display processor that generates output signals in a suitable form (e.g., RGB) for display by a display device 30 (e.g., a kinescope). The display processor 24 also provides vertical (V) and horizontal (H) blanking signals which are coupled via respective diodes D2 and D1 to an inhibit or blanking input 21 of the non-linear processor 20 for disabling the processor during blanking intervals.
In operation, a user provides operating choices to receiver control unit 32 having outputs connected to tuner 12, switch 14 and processor 18 for controlling, respectively, tuner channel selection, main and inset picture choices and functions such as inset picture on/off and control of the position of the inset picture within the main picture. Multiplex switch 22 inserts the inset picture video (Y2,C2) within the main picture video (Y1',C1 in which the luminance component has been non-linearly processed). The resultant picture in picture video (Y3,C3) is processed for display on kinescope 30 via display processor 24.